1. Field of the Invention
The present invention is related to telescopic boom devices, and more particularly to an improved telescopic boom guidance assembly for guiding the boom during telescopic movement.
2. Description of the Prior Art
Telescopic boom devices are commonly used in applications requiring rapid extension and retraction of a working tool. For example, telescopic booms are commonly used in underground mining operations for working on the ceiling or upper surface of the mine. These telescopic booms are provided with scaling tools which knock down loose deposits from the ceiling of the mine to stabilize the mine before workers are allowed to enter.
Telescopic boom devices typically include an elongated hollow outer boom, an elongated inner boom telescopically received within the outer boom, and a guidance system for guiding the inner boom for telescoping movement in and out of the outer boom. The guidance system typically includes a plurality of wheels welded to one end of the inner boom. The wheels engage a track or guide rail positioned in the outer boom for guiding the inner boom during telescopic movement. Prior art guidance systems also typically include a plurality of wheels welded to one end of the outer boom for engaging the outer surface of the inner boom during telescopic movement.
Prior art telescopic booms suffer from limitations which limit their utility. For example, it has been discovered in the industry that the guidance systems of prior art telescopic booms commonly fail. In particular, the wheels positioned on the inner booms frequently slide off of the truck or guide rails, thus rendering the telescopic boom inoperable. There are several limitations in the design of prior art telescopic boom guidance systems which cause this problem. For example, the wheels of prior art guidance systems present rail-engaging surfaces which are generally flat or have a radius of curvature which is significantly greater than the radius of curvature of the guide rails positioned in the outer boom. This results in limited surface contact between the wheels and the guide rails and causes the wheels to slide off of the guide rails.
Another limitation of prior art guidance systems is that their wheels only engage a small portion of the guide rails and do not include structure for maintaining the engagement between the wheels and the guide rails.
Another limitation of prior art guidance systems is that the wheels attached to the outer boom engage only a small portion of the outer surface of the inner boom. Accordingly, these wheels frequently slide off of the outer surface of the inner boom and render the telescopic boom inoperable.
Another limitation of prior art guidance systems is that the axles or shafts supporting the wheels are typically permanently welded to the inner and outer booms and thus are difficult to repair and replace.
Another limitation of prior art guidance systems is that they are difficult to adjust. Due to the harsh working environment, the inner booms often become deformed during normal operation. For example, the outer surface of the inner boom may become dented or may expand at certain points due to metal strain. These deformities cause alignment problems between the wheels of the guidance system and the guide rails. To realign the wheels to compensate for the deformities, the wheels must be cut from the inner boom, realigned and re-welded.
The limitations described above limit the utility of prior art telescopic booms. In particular, prior art telescopic booms commonly breakdown and thus require frequent repair. Due to their large size, telescopic booms typically must be removed from the mining site to repair. This results in lost productivity, increased costs, and shortened equipment life.
Accordingly, there is a need for an improved telescopic boom which overcomes the limitations of the prior art. More particularly, there is a need for a telescopic boom having a guidance system which more effectively maintains the telescopic engagement between the inner boom and the outer boom.